This invention relates to abrasive particles and methods of making the same. The abrasive particles can be incorporated into a variety of abrasive articles, including bonded abrasives, coated abrasives, nonwoven abrasives, and abrasive brushes.
In the early 1980""s a new and substantially improved type of alumina abrasive particles, commonly referred to as xe2x80x9csol gelxe2x80x9d or xe2x80x9csol gel-derivedxe2x80x9d abrasive particles, was commercialized. This new type of alpha alumina abrasive particle had a microstructure made up of very fine alpha alumina crystallites. The grinding performance of the new abrasive particle on metal, as measured, for example, by life of abrasive products made with the particles was dramatically longer than such products made from conventional, fused alumina abrasive particles.
In general, sol gel abrasive particles are typically made by preparing a dispersion or sol comprising water, alumina monohydrate (boehmite), and optionally peptizing agent (e.g., an acid such as nitric acid), gelling the dispersion, drying the gelled dispersion, crushing the dried dispersion into particles, calcining the particles to remove volatiles, and sintering the calcined particles at a temperature below the melting point of alumina Frequently, the dispersion also includes one or more oxide modifiers (e.g., CeO2, Cr2O3, CoO, Dy2O3, Er2O3, Eu2O3, Fe2O3, Gd2O3, HfO2, La2O3, Li2O, MgO, MnO, Na2O, Nd2O3, NiO, Pr2O3, Sm2O3, SiO2, SnO2, TiO2, Y2O3, Yb2O3, ZnO, and ZrO2), nucleating agents (e.g., xcex1-Al2O3, xcex1-Cr2O3, and xcex1-Fe2O3) and/or precursors thereof. Such additions are typically made to alter or otherwise modify the physical properties and/or microstructure of the sintered abrasive particles. In addition, or alternatively, such oxide modifiers, nucleating agents, and/or precursors thereof may be impregnated into the dried or calcined material (typically calcined particles).
Certain preferred alpha alumina-based abrasive particles are highly dense (i.e., greater than 95% of theoretical) and have a fine (e.g., submicrometer), uniform alpha alumina microstructure. Further, some preferred alpha alumina-based abrasive particles include oxide modifiers, as discussed above, which may, in some cases also include submicrometer oxides other than alpha alumina, wherein the latter may or may not be submicrometer. The grain size of the alpha alumina and other oxides, the oxide phases present in the abrasive particles, as well as the physical properties (e.g., density, hardness, and toughness) or characteristics may depend, for example, on the particular composition and/or process (including sintering time and temperature) used to make the abrasive particles. For example, longer sintering times and higher temperatures tend to provide higher density abrasive particles. However, longer sintering times and higher temperatures also tend to undesirably increase grain growth.
Sol-gel-derived alpha alumina-based sintered abrasive particles have been used in a wide variety of abrasive products (e.g., bonded abrasives, coated abrasives, and abrasive brushes) and abrading applications, including both low and high pressure grinding applications.
Even though there are a variety of abrasive particles known, including a number of sol-gel-derived abrasive particles, the abrasive industry continues to desire additional abrasive particles which may offer a performance advantage(s) in one or more applications.
In one aspect, the present invention provides a sintered alpha alumina-based abrasive particle comprising alpha alumina (in some embodiments, 55 to 97, or even 55 to 93 percent by weight), and, by weight, Gd2O3 in a range from 1 to 15 percent (in some embodiments, 2 to 8 percent), and ZnO in a range from 0.2 to 8 percent (in some embodiments, 1 to 5 percent), based on the total metal oxide content of the abrasive particle, and a Gd2O3 to ZnO molar ratio in a range from 2:1 to 1:5 (in some embodiments, in a range from 1:2 to 1:4, or even 1:2 to 1:3), wherein less than 0.05 (in some embodiments, less than 0.025, or even less than 0.01) volume percent of the alpha alumina present in the sintered alpha alumina-based abrasive particle was nucleated with a nucleating agent (i.e., material having the same or approximately the same crystalline structure as alpha alumina, or otherwise behaving as alpha alumina) itself (e.g., alpha alumina seeds, alpha Fe2O3 seeds, or alpha Cr2O3 seeds) or a precursor thereof; other nucleating agents may include Ti2O3 (having a trigonal crystal structure), MnO2 (having a rhombic crystal structure), Li2O (having a cubic crystal structure), and titanates (e.g., magnesium titanate and nickel titanate).
In another aspect, the present invention provides a method for making sintered alpha alumina-based abrasive particles according to the present invention, the method comprising:
preparing a dispersion by combining components comprising liquid medium, peptizing agent, boehmite, a Gd2O3 source (e.g., a gadolinium salt), and a ZnO source (e.g., a zinc salt);
converting the dispersion to particulate alpha alumina-based abrasive particle precursor material; and
sintering the particulate alpha alumina-based abrasive particle precursor material to provide the sintered alpha alumina-based abrasive particles.
In another aspect, the present invention provides a method for making sintered alpha alumina-based abrasive particles according to the present invention, the method comprising:
preparing a dispersion by combining components comprising liquid medium, peptizing agent and boehmite;
converting the dispersion to particulate alpha alumina-based abrasive particle precursor material;
calcining the particulate alpha alumina-based abrasive particle precursor material to provide first calcined alpha alumina-based abrasive particle precursor particles;
impregnating the first calcined particles with an impregnation composition comprising liquid medium to provide impregnated alpha alumina-based abrasive particle precursor particles;
calcining the impregnated alpha alumina-based abrasive particle precursor particles to provide second calcined alpha alumina-based abrasive particle precursor particles; and
sintering the second calcined particles to provide the sintered alpha alumina-based abrasive particles, wherein at least one of the dispersion or the impregnation composition comprise a Gd2O3 source (e.g., gadolinium salt) and a ZnO source (e.g., a zinc salt).
In this application:
xe2x80x9cBoehmitexe2x80x9d refers to alpha alumina monohydrate and boehmite commonly referred to in the art as xe2x80x9cpseudoxe2x80x9d boehmite (i.e., Al2O3.xH2O, wherein x=1 to 2).
xe2x80x9cAlpha alumina-based abrasive particle precursor,xe2x80x9d xe2x80x9cAbrasive particle precursorxe2x80x9d or xe2x80x9cunsintered abrasive particlexe2x80x9d refers to a dried alumina-based dispersion (i.e., xe2x80x9cdried abrasive particle precursorxe2x80x9d) or a calcined alumina-based dispersion (i.e., xe2x80x9ccalcined abrasive particle precursorxe2x80x9d), typically in the form of particles, that has a density of less than 80% (typically less than 60%) of theoretical, and is capable of being sintered or impregnated with an impregnation composition and then sintered to provide sintered alpha alumina-based abrasive particle.
xe2x80x9cSintered alpha alumina-based abrasive particlexe2x80x9d as used herein refers to an alpha abrasive particle that has been sintered to a density of at least 85% (preferably, at least 90% and more preferably, at least 95%) of theoretical, and contains, on a theoretical oxide basis, at least 60) by weight Al2O3.
xe2x80x9cDispersionxe2x80x9d or xe2x80x9csolxe2x80x9d refers to a solid-in-liquid two-phase system wherein one phase comprises finely divided particles (in the colloidal size range) distributed throughout a liquid. A xe2x80x9cstable dispersionxe2x80x9d or xe2x80x9cstable solxe2x80x9d refer to a dispersion or sol from which the solids do not appear by visual inspection to begin to gel, separate, or settle upon standing undisturbed for about 2 hours.
xe2x80x9cImpregnation compositionxe2x80x9d refers to a solution or dispersion of a liquid medium, and a typically a source of metal oxide that can be impregnated into an abrasive particle precursor.
xe2x80x9cImpregnated abrasive particle precursorxe2x80x9d refers to a dried alumina-based dispersion (i.e., xe2x80x9cimpregnated dried abrasive particle precursorxe2x80x9d) or a calcined alumina-based dispersion (i.e., xe2x80x9cimpregnated calcined abrasive particle precursorxe2x80x9d) that has a density of less than 80% (typically less than 60%) of theoretical, and has been impregnated with an impregnation composition, and includes impregnated dried particles and impregnated calcined particles.
xe2x80x9cSinteringxe2x80x9d refers to a process of heating at a temperature below the melting temperature of the material being heated to provide densification and crystallite growth to provide a tough, hard, and chemically resistant ceramic material. The sintered alpha alumina-based abrasive particle according to the present invention is not made by a fusion process wherein heating is carried out at a temperature above the melting temperature of the material being heated.
Abrasive particles according to the present invention are useful, for example, in loose form or used incorporated into abrasive articles. Abrasive articles according to the present invention comprise binder and a plurality of abrasive particles, wherein at least a portion of the abrasive particles are the abrasive particles according to the present invention. Exemplary abrasive products include coated abrasive articles, bonded abrasive articles (e.g., wheels), non-woven abrasive articles, and abrasive brushes. Coated abrasive articles typically comprise a backing having first and second, opposed major surfaces, and wherein the binder and the plurality of abrasive particles form an abrasive layer on at least a portion of the first major surface.
In some embodiments preferably, at least 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 55, 60, 65, 70, 75, 80, 85, 90, 95, or even 100 percent by weight of the abrasive particles in an abrasive article are the abrasive particles according to the present invention, based on the total weight of the abrasive particles in the abrasive article.
Abrasive particles are usually graded to a given particle size distribution before use. Such distributions typically have a range of particle sizes, from coarse particles fine particles. In the abrasive art this range is sometimes referred to as a xe2x80x9ccoarsexe2x80x9d, xe2x80x9ccontrolxe2x80x9d and xe2x80x9cfinexe2x80x9d fractions. Abrasive particles graded according to industry accepted grading standards specify the particle size distribution for each nominal grade within numerical limits. Such industry accepted grading standards (i.e., specified nominal grades) include those known as the American National Standards Institute, Inc. (ANSI) standards, Federation of European Producers of Abrasive Products (FEPA) standards, and Japanese Industrial Standard (JIS) standards. In one aspect, the present invention provides a plurality of abrasive particles having a specified nominal grade, wherein at least a portion of the plurality of abrasive particles are abrasive particles according to the present invention. In some embodiments preferably, at least 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 55, 60, 65, 70, 75, 80, 85, 90, 95, or even 100 percent by weight of the plurality of abrasive particles are the abrasive particles according to the present invention, based on the total weight of the plurality of abrasive particles.
In another aspect, the present invention provides a method of abrading a surface, the method comprising:
providing an abrasive article comprising a binder and a plurality of abrasive particles, wherein at least a portion of the abrasive particles according to the present invention;
contacting at least one of the abrasive particles according to the present invention with a surface of a workpiece; and
moving at least one of the contacted abrasive particles according to the present invention or the contacted surface to abrade at least a portion of the surface with the contacted abrasive particle according to the present invention.